This invention is concerned with an improved method of providing a multiple-channel recording and display capability. There is a present and continuing need for higher and higher speed information recording and display systems. To this end, prior art systems have been developed which have achieved significantly higher speed recording and display systems by use of lasers and acousto-optic modulator cells. It was realized that the inherent speed limitations of raster scan recording systems could be circumvented by use of multiple scanning beams and several prior art systems involving lasers, acousto-optic modulator cells and multiple scanning beams have been described. For example, U.S. Pat. No. 3,744,039 presents a multiple-channel information translation system wherein many amplitude modulated radio-frequency carrier signals of different predetermined frequencies are simultaneously impressed on the acousto-optic cell to create a multiplicity of angularly spaced output beams from a single input laser beam. Additionally, it was shown that such a system could be used with the addition of appropriate electronic circuits such as character generators to provide a high speed alphanumeric line printer capability.
It was recognized that the basic system described in the patent could have some limitations in that random, signal-related spurious amplitude modulation of the primary output light beams could result from cross-channel interference effects in the acousto-optic cell. In U.S. Pat. No. 3,935,566, entitled "Multiple-Channel Information Translation System and Method", methods are described for the selection of the various carrier frequencies which would suppress the spurious amplitude modulation of the primary beams.
A multiple-beam scanning and recording system, presented in U.S. Pat. No. 4,000,493 entitled "Acousto-Optic Scanner Apparatus and Method", avoids these spurious modulation effects by reducing the carrier signal levels to such a value so as to minimize cross-channel interference effects. Unfortunately, the conversion efficiency of the acousto-optic cell at these low drive levels is also quite low and in many systems where laser power is already barely sufficient to meet the system requirements, could represent an intolerable loss.
Another prior art system is described in U.S. Pat. No. 3,900,851 entitled "Multi-Channel Wideband Oscillograph". In this system, each of the simultaneously applied carrier frequencies are frequency modulated to provide multiple, simultaneous oscillograph traces. This system has several disadvantages. First, it has been demonstrated experimentally that the conversion efficiency of an acousto-optic modulator cell decreases as the number of simultaneously applied carrier frequencies is increased. Second, intermodulation effects in the external electronic circuits and in the acousto-optic cell itself could create spurious oscillograph traces.
All of the prior art systems cited above feature simultaneous application of multiple modulated carrier frequencies to the acousto-optic cell to achieve multiple beam operation and consequently have the disadvantages of reduced conversion efficiencies and possible interference effects.